Tom makes a good point about the air flow to water flow ratio! I can estimate my ratio for a single vertex diffuser at 7 feet deep by the following...
7 foot deep yields 3.5 psi PLUS a little backpressure (1.5psi) from the length/size of tubing that I use PLUS 1 psi for the diffuser itself. In total = 6psi. This jives with the pressure gage on my system pretty close. From the chart below using the top right graph...
...we can see that my pump puts out about 4 CFM of air. That's the first part of the ratio. Using the Vertex chart above, my single diffuser would move about 1200 GPM at 7 feet deep. Converting to CFM...1200 GPM/7.48 G/CF = 160 CFM of water.
Ratio of Pump Air to Water Movement (in CFM at 7 feet deep) is 4:160 OR 1 to 40.
I'm not sure what this mumbo jumbo is good for unless you can somehow equate your diffuser to the vertex one and know the air flow at the depth of your diffuser.
One of the reasons I bought Vertex was the fact that they had some mumbo jumbo numbers to fiddle with cause that's what I do.
Do you have a pump chart? I am almost 100% sure it puts out more air at shallower depths and if we could somehow compare a bubble boil between yours and a vertex one we could guestimate the water movement, albeit very crude, but better than what the company has given you so far.
